nfc: fdp: correct kerneldoc for structure

Since structure comments are not kerneldoc, remove the double ** to fix
W=1 warnings:

    warning: This comment starts with '/**', but isn't a kernel-doc comment.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210528124200.79655-1-krzysztof.kozlowski@canonical.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>